The energy storing reaction that is of greatest importance in artificial photosynthesis is the decomposition of water into its constituent elements, H2 and O2, with the former as the fuel. As a redox reaction, water splitting can be divided into its two half-cell components for separate investigation and development. Despite great efforts over the past decade, neither half-reaction has been carried out photochemically in a system composed of earth-abundant elements with both an activity and robustness of the type needed for further development. Homogeneous systems for light-driven reduction of protons to H2 typically suffer from short lifetimes because of decomposition of the light-absorbing molecule and/or catalyst, if present.
Molecular hydrogen (H2) is a clean-burning fuel that can be produced from protons (H+) in the reductive half-reaction of artificial photosynthesis (AP) systems. One of the strategies for light-driven proton reduction features a multicomponent solution with a light absorbing molecule (chromophore) that transfers electrons to a catalyst that reduces protons. However, these solution systems often use nonaqueous solvents, and always have short lifetimes from decomposition of the chromophore over a period of hours. This difficulty has led to more complicated architectures that separate the sites of light absorption and proton reduction. Heterostructures between NCs and traditional precious metal nanoparticle H2 production catalysts, and between NCs and iron-hydrogenases, have produced proton reduction in solution.